being a sophisticated arborist, you’re unlikely to plant your trees in either a sparse grid or a dense megacluster. Instead, you choose to plant groves of densely planted trees interspersed with roads, which not only provide you access to the interior of your property but act as firebreaks, separating one part of the crop from another and insuring the whole from a fire in one of its parts.

Many of the world’s most critical systems—from coral reefs and communities to businesses and financial markets—have similar robust-yet-fragile dynamics; they’re able to deal capably with a range of normal disruptions but fail spectacularly in the face of rare, unanticipated ones.

A perfectly efficient system, like the densely planted tree farm, is also the most susceptible to calamity; a perfectly robust system, like the sparsely planted tree farm, is too inefficient to be useful.